One piece Flexible Skateboard

ABSTRACT

A flexible skateboard may include a pair of direction casters mounted for steering rotation on a flexible skateboard, twistable for propulsion. One or more vertical wall supports may be provided to resist bowing. Centering spring arrangements including range or rotation limitations such as hard stops may be included. One or two dual wheel assemblies may be exchanged for the single wheel assemblies for ease or riding or learning how to ride. One piece skateboard bodies may be formed by rigidly connecting together multiple pieces of the same or similar wooden or plastic molded parts to form a bridge like connecting member having increased structural rigidity and strength for its weight.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/539,550 filed Mar. 6, 2007, now U.S. Pat. No. ______, which claimsthe priority of the filing date of U.S. Provisional application Ser. No.60/087,970 filed Aug. 11, 2008 and Ser. No. 61/118,345 filed Nov. 26,2008, and is a continuation in part of U.S. patent application Ser. No.11/687,594 filed Mar. 6, 2007 now U.S. Pat. No. 7,766,351, which is acontinuation of U.S. PCT patent application Ser. No. 07/646,672 filedMar. 22, 2007, which is a continuation in part of U.S. patentapplication Ser. No. 11/462,027 filed Aug. 2, 2006, now U.S. Pat. No.7,338,056, which claims the priority of the filing date of U.S.Provisional application Ser. No. 60/795,735, filed Apr. 28, 2006.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention is related to skateboards such as skateboards in whichone end of the skateboard may be twisted or rotated, with respect to theother end, by the user and in particular to skateboards with wheelcentering springs.

2. Description of the Prior Art

Various skateboard designs have been available for many years.Conventional designs typically require the user to lift one foot fromthe skateboard to push off on the ground in order to provide propulsion.Such conventional skateboards may be steered by tilting the skateboardto one side and may be considered to be non-flexible skateboards.Skateboards have been developed in which a front platform and a rearplatform are spaced apart and interconnected with a torsion bar or otherelement which permits the front or rear platform to be twisted orrotated with respect to the other platform. Such platforms havelimitations, including complexity, limited control or configurability offlexure and cost. What is needed is a new skateboard design without suchlimitations.

SUMMARY OF THE DISCLOSURE

A skateboard is disclosed having a skateboard platform of flexiblematerial. A vertical support is affixed to the platform to resist bowingfrom the weight of a rider. A pair of wheels, each supporting one end ofthe platform are mounted for rotation about a steering axis and about arotational axis. Twisting of the platform ends in opposite directions bythe rider propels the skateboard. The vertical support may be a verticalwall extending below the platform along part or all of the platformperiphery.

The steering axis of one or both wheels may be at an acute angle to asurface of the platform and may be at the same acute angle to thesurface of the platform. The rotational axis of one or both wheels maybe a distance from the steering axis of that wheel. A spring resistingsteering may be mounted about the steering axis of one or both wheels sothat the wheel(s) can be centered by the spring(s). A pair of stops maybe fixedly mounted to the platform and at least one limit stop mountedfor steering rotation with one of the wheels to prevent rotation thereofbeyond a preset limit.

The skateboard may include additional vertical supports below theplatform. The flexible material may be molded plastic and the wall andplatform may be formed of the same material or wood.

A skateboard may include a flexible, molded plastic skateboard, avertical support molded to and extending below the platform, thevertical support resisting bowing from the weight of a rider andresisting twisting by the rider. A pair of wheels, each supporting oneend of the platform may be mounted for steering rotation about asteering axis at an acute axis to the platform and for rotation about arotational axis at a distance from the steering axis so that twisting ofthe platform ends in opposite directions by the rider propels theskateboard.

The vertical support may be a vertical wall extending below the platformalong a periphery thereof. A spring may be provided to resist steeringrotation of one or both of the wheels to center the steering rotationwhen not in contact with the ground. The spring may be mounted aroundthe steering axis. A pair of stops may be fixedly mounted to theplatform and at least one limit stop mounted for steering rotation withone of the wheels to prevent steering rotation of said wheel beyond apreset limit.

A skateboard is disclosed having a skateboard platform of flexiblematerial with first and second foot support areas on a first surface ofthe board. A vertical support wall is affixed along a periphery of theplatform, the wall resisting bowing from the weight of a rider and alsoresisting twisting of the platform along a longitudinal axis between thefirst and second foot support areas. A first wheel supporting the firstfoot support area is provided, the first wheel mounted for rotationabout a first steering axis and for rotation about a first rotationalaxis. A second wheel supporting the second foot support area isprovided, the second wheel mounted for rotation about a second steeringaxis and for rotation about a second rotational axis. Twisting of thefoot support areas in opposite directions along the longitudinal axis bya rider propels the skateboard.

The first axis may be at a first acute angle to the first surface. Thesecond axis may be at a second acute angle to the first surface. Thefirst and second axes may be parallel. The first and second acute anglesmay be equal. The first rotational axis may be a first distance from thefirst steering axis. The second rotational axis may be a second distancefrom the first steering axis and the first and second distances may beequal.

A spring resisting steering of the first wheel about the steering axismay be provided so that the first wheel becomes aligned with motion ofthe skateboard when the skateboard is not being twisted by the rider.The spring may be mounted around the steering axis. A pair of stops maybe fixedly mounted to the platform and at least one limit stop may bemounted for steering rotation with the first or second wheel to preventrotation of said wheel beyond a preset limit.

The skateboard may include a narrow central section between the firstand second foot support areas which may resist twisting more than thenarrow central section. There may be additional vertical supports belowthe platform. The wall and platform may be formed of the same material,such as molded plastic or wood.

A skateboard is disclosed including a one piece flexible skateboardplatform having first and second foot support areas aligned along alongitudinal axis, a pair of wheel assemblies, each including a bearinghaving inner and outer bearing races, a wheel housing supporting atleast one wheel for rotation about a rotational axis, the wheel housingsecured to the outer bearing race for steering rotation therewith withrespect to the inner bearing race about a pivot axis at the acute angle,a pair of fixed stops securing the inner race of said at least one ofthe wheel housing to the platform at an acute angle, and at least onelimit stop mounted for rotation with said at least one of the wheelhousings for preventing steering rotation of that wheel housing beyond apresent limit by interaction with one of the pair fixed stops.

Each of the pair of wheel assemblies may include a pair of fixed stopssecuring the inner race of the bearing in that wheel assembly to theplatform at an acute angle. A bearing cap may be included on which thepair of fixed stops are mounted. The bearing cap may have a peripheraltool surface at least partway around an edge of the bearing cap for usein securing the bearing cap, wherein said pair of fixed stops areportions of said bearing cap edge. The fixed stops and the limit stopmay include contact areas which are at a first radius from said pivotaxis. A rod at least partially externally threaded rod at one end havinga peripheral tool surface for use in securing the partially externallythreaded end of the rod to the skateboard platform may be included andthe rod may have an internal threaded opening at second end for mountingthe wheel assembly thereto.

At least one or both of said wheel housings may include a common wheelaxle aligned with said rotational axis and a pair of wheels mounted onsaid common axis for rotation. The one piece flexible skateboard mayinclude a central area rigidly mounted to both the first and second footsupport areas so that the skateboard flexes as a single unit. Thecentral area may include a plurality of longitudinal elements generallyaligned with the longitudinal axis mounted to both the first and secondfoot support areas so that the skateboard flexes as a single unit and/orplurality of structural elements rigidly mounted to each of theplurality of longitudinal elements to resist bowing of the skateboardfrom a user's weight.

The plurality of longitudinal structural elements may each rigidlyfastened to each of the plurality of longitudinal elements. Thelongitudinal elements may have a surface generally common with surfacesof the first and second foot support areas. One of the longitudinalelements may bowed in a downward direction between the foot supportareas to further resist bowing of the skateboard from the user's weight.

The central area may flex more than the first and second foot supportareas when a user twists the foot support areas in opposition directionsabout the longitudinal axis. Twisting of the foot support areas inopposite directions by the user may cause rotation of the wheels in thesame direction to move the skateboard in that direction and may move theskateboard from a standing start.

A flexible skateboard is disclosed having a one piece platform formed ofa material twistable along a twist axis, the material formed to includea pair of foot support areas along the twist axis, generally at each endof the platform, to support a user's feet and a central section betweenthe foot support areas and a pair of caster assemblies, each having asingle caster wheel mounted for rolling rotation, each caster assemblymounted at a user foot support area for steering rotation about one of apair of generally parallel pivot axes each forming a first acute anglewith the twist axis. The central section of the platform material may beconfigured to be sufficiently narrower than the foot support areas topermit the user to add energy to the rolling rotation of the casterwheels by twisting the platform alternately in a first direction andthen in a second direction while the foot support areas.

A multi-arm spring assembly is provided to cause each caster wheel toreturn to a neutral steering, straight ahead position when steeringforces are removed, for example when the wheel becomes airborne. Eachspring arm works against a stop which pivots with the wheel and a stopwhich does not pivot with the wheel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric view of the top of one piece flexible skateboard10.

FIG. 2 is a side view of skate board 10.

FIG. 3 is an isometric view of the bottom of one piece flexibleskateboard 10.

FIG. 4 is an isometric view of a portion of the bottom of boardillustrating a removably mounted wedge 32.

FIG. 5 is a graphical illustration of a skateboard twisting in a firstdirection.

FIG. 6 is a graphical illustration of a skateboard twisting in a seconddirection.

FIG. 7 is a graphical illustration of the twisting of board 10 having afirst configuration.

FIG. 8 is a graphical representation of the twisting of board 10 havinga second configuration to provide a different flexing function inresponse to applied twisting forces.

FIG. 9 is a graphic representation of the force applied to a one pieceflexible skateboard as a function or twist or rotation of the board.

FIG. 10 is an isometric view of a portion of the underside of board 10including removably installed elastomeric wedges 82 used to adjust theboard flexing function.

FIG. 11 is a partial view of a self centering front section 84 of board10.

FIG. 12 is a top view of a caster wheel assembly with an external selfcentering torsion spring.

FIG. 13 is a partial side view of a caster wheel assembly with aninternal self centering torsion spring.

FIGS. 14A and 14B are graphical representations of board twist as afunction of differential force or pressure applied by a user. FIG. 14Cis a graphical representation of relative twist along the foot supportand central areas of the board.

FIG. 15 is a graphical representation of caster wheel assemblies 24 and26 with non-differential pressure or forces applied by a user along thetwist axis 28.

FIG. 16 is a graphical representation of caster wheel assemblies 24 and26 with differential pressures or forces applied by a user on eitherside of twist axis 28.

FIG. 17 is a graphical illustration of the steering of wheel assemblies24 and 26 with non-differential pressures or forces applied by a user onone side of twist axis 28.

FIG. 18 is a graphical illustration of the steering of wheel assemblies24 and 144 having non-parallel pivot axes with non-differentialpressures or forces applied by a user on one side of twist axis 28.

FIG. 19 is a graphical illustration of the steering of wheel assemblies24 and 26 having parallel pivot axes with differential pressures orforces applied by a user on both side of twist axis 28.

FIG. 20 is a side view of an alternate embodiment in which one pieceflexible skateboard 146 is formed by molded wooden deck 148 providedwith integral kick tail 150.

FIG. 21 is a front view of a cross section of skateboard 146, takenalong line AA as shown in FIG. 20.

FIG. 22 is a top view of wooden platform 148 illustrating overall shapeincluding a top view of kick tail 150.

FIG. 23 is an isometric view of skateboard 146 including kick tail 150.

FIG. 24 is a top view of an alternate embodiment in which skateboard 160may include a pair of center section inserts 162 and 164 in platform 166for controlling the flexure of platform 166.

FIG. 25 is a top view of an alternate configuration of skateboard 160shown in FIG. 24 in which a single center section insert may beemployed.

FIG. 26 is a top view of an alternate configuration of skateboard 170including a textured surface and a series of partial peripheral wells inwhich inserts, such as rubber gripper bar inserts 188, 190, 192 and 194may be positioned.

FIG. 27 is a side view of skateboard 170 shown in FIG. 26.

FIG. 28 is a bottom view of skateboard 170 shown in FIG. 26.

FIG. 29 is a cross sectional view along line AA in FIG. 27.

FIG. 30 is an isometric view of a further embodiment of wheel assembly86 of FIG. 1 with an alternate centering spring arrangement.

FIG. 31 is an exploded view of wheel assembly 218 of FIG. 30.

FIG. 32 is an exploded view of spring and bearing assembly 220 of FIG.31.

FIG. 33 is a cutaway view of wheel assembly 218 of FIGS. 30 and 3

FIG. 34 is a perspective view of an alternate multi-arm spring returnassembly.

FIG. 35 is an exploded view of the multi-arm spring assembly of FIG. 34.

FIG. 36 is a partially cutaway view of the multi-arm return springassembly in the neutral or straight ahead orientation.

FIG. 37 is a view of the spring assembly of FIG. 36 in a steeredorientation.

FIG. 38 is a schematic view of the multi-arm spring assembly.

FIGS. 39 and 40 are illustrations of spring and bearing assembly 264 ina partially cutaway portions of fork 224.

FIGS. 41 a-41 c are illustrations of a top view of the operation of oneembodiment of a multi-arm coil centering spring wheel housing assembly.

FIGS. 42 a-c are illustrations of a top view of the operation of oneembodiment of a bearing cap and limit stop to control the maximumsteering angle of the wheel housing assembly.

FIG. 43 is an illustration of non-rotating shaft 290.

FIG. 44 is a top view of a dual wheel assembly used in one alternateembodiment.

FIG. 45 is a top view of an alternate embodiment of the dual wheelassembly shown in FIG. 44.

FIG. 46 is a side view of the dual wheel assembly shown in FIG. 45.

DETAILED DISCLOSURE OF THE PREFERRED EMBODIMENT(S)

Referring now to FIG. 1, flexible skateboard 10 is preferably fabricatedfrom a one piece, molded plastic platform 12 which includes foot supportareas 14 and 16 for supporting the user's feet about a pair ofdirectional caster assemblies mounted for pivoting or steering rotationabout generally parallel, trailing axes. Each caster assembly includes asingle caster wheel mounted for rolling rotation about an axlespositioned generally below the foot support areas. Skateboard 10generally includes relatively wider front and rear areas 18 and 20, eachincluding one of the foot support areas 14 and 16, and a relativelynarrower central area 22. The ratio of the widths of wider areas 18 and20 to narrow central area 22 may preferably be on the order of about 6to 1. Wheel assemblies 24 and 26 are mounted below one piece platform 12generally below foot support areas 14 and 16.

In operation, the skateboard rider or user places his feet generally onfoot support areas 14 and 16 of one piece platform 12 and can ride oroperate skateboard 10 in a conventional manner, that is as aconventional non-flexible skateboard, by lifting one foot from board 10and pushing off against the ground. The user may rotate his body, shifthis weight and/or foot positions to control the motion of theskateboard. For example, board 10 may be operated as a conventional,non-flexible skateboard and cause steering by tilting one side of theboard toward the ground. In addition, in a preferred embodiment, board10 may also be operated as a flexible skateboard in that the user maycause, maintain or increase locomotion of skateboard 10 by causing frontand rear areas 18 and 20 to be twisted or rotated relative to each othergenerally about upper platform long or twist axis 28.

It is believed by applicants that the relative rotation of differentportions of platform 12 about axis 28 changes the angle at which theweight of the rider is applied to each of the wheel assemblies 24 and 26and therefore causes these wheel assemblies to tend to steer about theirpivot axes. This tendency to steer may be used by the rider to addenergy to the rolling motion of each caster wheel about its rolling axleand/or to steer.

As a simple example, if the user or rider maintained the position of hisrearward foot (relative to the intended direction of motion of board 10)on foot support area 16, generally along axis 15 and parallel to theground, while maintaining his front foot in contact with support area14, generally along axis 13 while lowering, for example, the ball of hisfront foot and/or lifting the heal of that foot, front section 18 ofboard 10 would tend to twist clockwise relative to rear section 20 whenviewed from the rear of board 10. This twist would result in the tiltingright front side 30 of board 10 in one direction, causing the weight ofthe rider to be applied to wheel assembly 24 at an acute angle relativeto the ground rather than to be applied orthogonal to the ground, andwould therefore cause wheel assemblies 24 and 26 to begin to roll,maintain a previous rolling motion and/or increase the speed of motionof the board 10 e.g. by adding energy to the rolling motion of thewheels.

In practice, the rider can cause the desired twist of platform 12 ofboard 10 in several ways which may be used in combination, for example,by twisting or rotating his body, applying pressure with the toe of onefoot while applying pressure with the heel of the other foot, bychanging foot positions and/or by otherwise shifting his weight. Toprovide substantial locomotion, the rider can first cause a twist alongaxis 28 in a first direction and then reverse his operation and causethe platform to rotate back through a neutral position and then into atwist position in the opposite direction. Further, while moving forward,the rider can use the same types to motion, but at differing degrees, tocontrol the twisting to steer the motion of board 10. The ride can, ofcourse, apply forces equally with both feet to operate board 10 withoutsubstantial flexure.

Wider sections 18 and 20 have an inherently greater resistance totwisting about axis 28 than narrower section 22 because of the increasedstiffness due to the greater surface area of the portions to be twisted.That is, narrower section 22 is narrower than wider sections 18 and 20.The resistance of the various sections of platform 12 to twisting canalso be controlled in part by the choice of the materials, such asplastic, used to form platform 12, the widths and thicknesses of thevarious sections, the curvature if any of platform 12 along axis 28 oralong any other axes and/or the structure and/or cross section shape ofthe various sections.

Referring now to FIG. 2, skateboard 10 may include sidewalls 62 and/orother structures. Sidewalls 62 may be increased in height, e.g.orthogonal to the top surface 58 of platform 12, in the central portionof central area 22 to provide better vertical support if required. In apreferred embodiment, the height of sidewall 62 in central area 22varies from relatively tall in the center of board 10 to relativelyshorter beginning where areas 18 and 20 meet central area 22. The ratioof the sidewall height “H” in central section 22, to the side wallheights in wider areas 18 and 20 may preferably be on the order of about2 to 1.

As shown in FIG. 2, wheel assemblies 24 and 26 may be substantiallysimilar. Wheel assembly 24 may be mounted—for rotation about axis 34—toan inclined or wedge shape wheel assembly section 32 by securing pivotaxle or shaft 41 (visible in FIG. 4) in a suitable opening in wedge 32.The rotation of wheel assembly 24 about axis 34 may preferably belimited, for example, within a range of about ±180°, and more preferablywithin a range of about ±160°, to improve the handling and control ofboard 10. Each direction caster may include a tension, compression ortorsional spring to provide self-centering, that is, to maintain thealignment of wheels 36 along axis 28 (visible in FIG. 1) as shown anddescribed for example with reference to FIG. 13 below.

A pair of wedges 32 and 48 may be formed in platform 12 and include ahole for wheel assembly axle 41 mounted along axis 34. Alternately,wedges 32 and 48 may be formed as separate pieces from platform 12 andbe connected thereto during manufacture of board 10 by for examplescrews, clips or a snap in arrangement in which the upper surfaces ofwedges 32 and 48 are captured by an appropriate receiving section moldedinto the lower face of platform 12. Wedge 32 may be used to incline axis34, about which each caster may pivot or turn, with respect to the uppersurface 58 of platform 12 at an acute angle θ1 which may preferably bean angle of about 24°.

Wheel assembly 24 may include wheel 36 mounted on hub 38 which ismounted to axle 40 for rotation, preferably in bearings. Axle 40 ismounted in fork 96 of caster frame 42. A bearing or bearing surface maypreferably be inserted between caster frame 42 and wedge 32, or formedon caster frame 42 and/or wedge 32 and is shown as bearing 46 in wheelassembly 26 mounted transverse to axis 50 in wedge 48 in rearmost widersection 20. Wheel assemblies 24 and 26 are mounted along axes 34 and 50each of which form an acute angle, θ1 and θ2 respectively, with theupper surface of platform 12. In a preferred embodiment, θ1 and θ2 maybe substantially equal. The use of identical wheel assemblies for frontand rear reduces manufacturing and related costs for board 10. Thecenter of foot support 14 may conveniently be positioned directly aboveaxis 40 in wheel assembly 24 and center of foot support 16 may bepositioned similarly above the axis of rotation of the wheel in wheelassembly 26.

During operation, users may shift their feet from foot positions 14 and16 toward central area 22 which as described above is a narrower andtherefore more easily twisted portion of platform 12. In order toprovide addition vertical strength to support the weight of one of theuser's feet, taller sidewalls 62 may be used in central section 22 asshown. In a preferred embodiment, the height of sidewalls 62 maygenerally rise in a gently curved shape from wider support areas 18 and20 to a maximum generally in the center of central section 22.

Platform 12 of board 10 is in a generally horizontal rest or neutralposition, e.g. in neutral plane 17, when no twisting force is applied toplatform 12 of board 10. This occurs, for example, when the rider is notstanding on board 10 or is standing in a neutral position. When board 10is in the neutral position, axes 34 and 50, angles θ1 and θ2 and boardaxis 28 (shown in FIG. 1) are all generally in the same plane orthogonalto neutral plane 17 of the top of platform 12, while axes 13 and 15 arein neutral plane 17. Upper surface 58 may not be flat and in a preferredembodiment, toe or leading end 60 and heel or trailing end 62 of surface58 may have a slight upward bend or kick as shown. In a preferredembodiment, central section 22 flares out at each end to wider sections18 and 20 while wider front section 18 may be slightly longer than rearsection 20. When a twisting force is applied to board 10, one or more ofaxes 34 and 50 move out of the vertical plane as described below ingreater detail with respect to FIG. 5.

Referring now to FIG. 3, an isometric view of the bottom of skate board10 is shown including platform 12, wider sections 18 and 20 and narroweror midsection 22. Wheel assemblies 24 and 26 are mounted to inclinedwedges 32 and 48 which are shown as molded-in portions of platform 12.Platform 12 may include a generally flat upper surface 58, (also shownin FIG. 2) as well as a wall portion 62 formed generally at a rightangle to layer 58. Peripheral sidewall 62 may have a constant crosssectional width, ‘w’, but in a preferred embodiment the height “H” ofwall 62 (also shown in FIG. 2) may vary for example to increasegenerally in midsection 22 in order to provide additional verticalsupport for the user when and if the user place some of his weight onmidsection 22. The sections of sidewall 62 with increased height inmidsection 22 are shown as starboard wall section 54 and port wallsection 52. Wall sections 52 and 54 may also have transverse wallmembers, such as full or partial cross brace or rib 56, which serve toboth provide additional vertical support if needed and to increase theresistance to twisting of various portions of board 10 about axis 28.

Referring now to FIG. 4, an exploded isometric view of rear section 20of an alternate embodiment of board 10 is shown in which each inclinedwedge 32 is formed as a separate piece from platform 12 and mountedthereto by any convenient means such as screws 64 which may be insertedthrough holes 66 in appropriate locations in platform 12 to mate withholes 68 in inclined wedge 32. Screws 64 may be self threading orotherwise secured to wedge 32. Frame 42 of wheel assembly 26 includescaster top 70 and bearing cap 95 forming top bearing 110, shown below ingreater detail in FIG. 13, and pivot axle 41—a top portion of which isreceived by and mounted in a suitable opening in wedge 32—to support therotation of wheel assembly 26 about axis 34. Axle 40 is mounted in fork96 of frame 42. Wheel 36 is mounted on hub 38 which is mounted forrotation about axle 40.

Wedge 32 may also be further secured to platform 12 by the action ofslot 72 which captures a feature of the bottom surface of platform 12such as transverse rib 74. As shown, wedge 32 may be convenientlymounted to and dismounted from platform 12 permitting replacement ofwedge 32 by other wedges with potentially different configurationsincluding different angles of alignment for axis 34 and/or othercharacteristics.

Referring now to FIG. 5, a graphical depiction of the motions ofportions of platform 12 are shown. Neutral plane 17 is shown in thehorizontal position indicating top surface 58 of platform 12 when notwisting forces are applied to skate board 10. Axis 28, along thecenterline of top surface 58 of platform 12, is shown orthogonal to thedrawing, coplanar with and centered in neutral plane 17. Axis 13 isshown as a solid line and represents the location of a cross section ofthe top surface of platform 12 at front foot position 14 in wide forwardsection 18 when the port side of wide section 18 is depressed below thehorizontal or neutral plane 17 for example by the user pressing down onthe port side and/or lifting up of the starboard side of foot position14. Axis 15 is shown as a dotted line, to distinguish it from axis 13for convenience, and represents the location of a cross section of thetop surface of platform 12 at rear foot position 16 in wide aft section20 of platform 12 when the starboard side of wide section 20 isdepressed below the horizontal or neutral plane 17 for example by theuser pressing down on the starboard side and/or lifting up of the portside of rear foot position 16. Thus FIG. 5 represents the relativeangles of wider front and rear sections 18 and 20 of platform 12 whenthe user has completed a maneuver in which he has twisted wider frontand rear sections 18 and 20 in opposite directions to a maximumrotation.

Wheel assembly 24 is shown mounted for rotation about axis 34. Axis 34of front wheel assembly 24 remains orthogonal to axis 13 of footposition 14. Similarly, wheel assembly 26 is shown mounted along axis50. Axis 50 of rear wheel assembly 26 remains orthogonal to axis 15 offoot position 16. For ease of illustration, wheel assemblies 24 and 26are depicted in cross section without rotation of the wheel assembliesabout axes 34 and 50.

In the position shown in FIG. 5, wheel assemblies 24 and 26 havepresumably been rotated from vertical positions to the opposite outwardpositions by action of the user in twisting board 10. It must be notedthat front and rear wheel assemblies 24 and 26 are able to rotate orpivot about their respective axes 34 and 50. During the twisting ofboard 10, wheel assemblies 24 and 26 rotate about the central axes ofthe wheels as long as such rotation takes less force than would berequired to skid the wheel assemblies into the positions as shown. Thedirection of this rotation is not random, but rather controlled byangles θ1 and θ2 between axes 34 and 50 and platform 12.

The view shown in FIG. 5 is looking at the front of board 10 so thataxes 34 and 50 are at right angles to one of the portions of platform12. A side view of the board 10, as shown for example in FIG. 2,illustrates that each wheel assembly is mounted for pivotal rotationabout an axis at an acute trailing angle to platform 12. The rotation ofthe wheels about each wheel axis of the wheel assemblies, combined witha slight rotation of each wheel assembly about its axis 34 or 50 whenthe ends of board 10 are twisted in opposite directions, causes,maintains or increases forward motion or locomotion of board 10 becauseaxes 34 and 50 are inclined so that each wheel assembly is in a trailingconfiguration, aft of the point at which each axis penetrates board 12from below. That is, axes 34 and 50 about which each wheel assemblyturns are both inclined in the same direction, preferably at a trailingangle with respect to the direction of travel and are preferablyparallel or nearly so.

Referring now to FIG. 6, axes 13 and 15 are shown in the oppositepositions than shown in FIG. 5, which would result from the userreversing his foot rotation, i.e. by twisting the front and rearsections of board 10 by pushing down and/or lifting up opposite of theway done to cause the twisting shown in FIG. 5. However, the combinationof the rotation of the wheels and the rotation of the wheel assembliesadds to the forward locomotion because axes 34 and 50 are in a trailingposition relative to the forward motion of board 10.

Referring now to FIG. 7, the solid line is a graphical representation ofthe twisting rotation as a function of time of point 74 (shown in FIGS.1 and 5) at a forward port side edge of wide section 18 during thetwisting motions occurring to board 10 as depicted in FIGS. 5 and 6.Point 74 may be considered to be the point at which axis 13 intersectsthe port side edge of platform 12. At some instant of time, such as t0,point 74 is at zero rotation. As the port side of forward wide section18 is rotated downward by force applied by the user, point 74 rotatesdownward until the maximum force is applied by the user and point 74reaches a maximum downward rotation at some particular time such as timet1. Thereafter, as the downward force applied by the user to theportside of forward section 18 decreases, the downward angle of rotationof point 74 decreases until at some time t2, point 74 returns to aneutral rotational position at a rotational angle of 0.

Thereafter, downward pressure can be applied by the user to thestarboard edge of section 18, e.g. in foot position 14, to cause point74 on the port side to twist or rotate upwards, reaching a maximum forceand therefore maximum rotation at time t3 after which the force may becontinuously reduced until neutral or zero rotation is reached at timet4. Similarly, as shown by the solid line in FIG. 7, the user can applyforces in the opposite direction to rearward wide section 20 so thatpoint 76, at the rearward port side of foot position 16, rotates fromthe neutral position at time t0, to a maximum upward rotation at timet1, through neutral at time t2, to a maximum downward rotation at timet3 and back to neutral at time t4.

Referring now to FIG. 8, the amount of force that must be applied by theuser to cause a particular degree of twist may correlate to the amountof control the user has with board 10. It may be desirable for therelationship between force and rotation to be varied as a function ofrotation or force. For example, in order to achieve a “stiff” boardwhile permitting a large range of total twist without requiring undoforce, the shape of platform 12 may be configured so that the amount offorce required to twist the board from the neutral plane seemsrelatively high to the user (at least high enough to be felt asfeedback) even if the additional force required to continue rotatingeach section of the board past a certain degree of rotation seemsrelatively easier to the user. Further, as an added safety and controlmeasure, the additional force required to achieve maximum rotation maythen appear to the user to increase greatly. As shown in FIG. 8, theshape of the graphs of the rotation of points 74 and 76, for the sameforces applied as function of time used to create the graph in FIG. 7,may be different providing a different feel to the user.

Referring now to FIG. 9, the concept just discussed above may be viewedin terms of a graph of force applied by the user as a function ofdesired rotation. The control feel desired for a skate board is notnecessarily an easily described mathematical function of force torotation. For some particular configuration of platform 12, withspecific shapes and relationships between the front and rear wide areasand the central narrow area, and specific shapes and sizes of sidewalls,ribs, surface curves and other factors, there will be a particular wayin which the board feels to the user to behave. That is, the feel of theboard and especially the user's apparent control of the board, inpreferred embodiments, is dependent on the shape and other boardconfiguration parameters. For simplicity of this description, oneparticular board configuration may be said to have a “linear” feel, thatis, the user's interaction with the board may seem to the user to resultin a linear relationship between force applied and rotation or twistachieved. In practice, this feel is very subjective but none the lessreal although the actual mathematical relationship may not be linear. Asa relative example, line 78 may represent a linear or other type ofboard having a first configuration of platform 12.

The shape and configuration of platform 12 may be adjusted, for example,by reducing the length of narrow section 22 along axis 28 (shown anddescribed for example with reference to FIG. 1) and/or changing thetaper of the transitions areas between narrow section 22 and front andrear wide sections 18 and 20. For a particular configuration of platform12, lengthening the relative length of narrow section 22 may result in aperceived sloppiness of control by the user while shortening therelative length of narrow section 22 may result in a greater difficultyin achieving any rotation at all. A similar effect may be obtained byadjusting the width of central section 22 relative to wider sections 18and 20. Line 80 represents a desired control relationship between forcerequired and angle achieved by a particular configuration of platform12. A more detailed example of twist as a function of force applied isshown below in FIGS. 14A and 14B and described for example with respectto FIGS. 14-19.

It is important to note that one advantage of the use of one pieceplatform 12 made of a plastic, twistable material formed in a moldingprocess, is that the desired feel or control of the board can beachieved by reconfiguration of the mold for the one piece platform.Although it may be difficult to predict (with mathematical precision),the shape and configuration of platform 12 needed to achieve a desiredfeel, it is possible to iteratively change the shape and configurationof platform 12 by modifying the mold in order to develop a desirableconfiguration with an appropriate feel. In particular, the relationshipbetween force applied and twist or rotation achieved by flexible skateboard 10 is function of the relative widths, shapes and otherconfiguration details of platform 12.

Platform 12 may be molded or otherwise fabricated from flexible PU-typeelastomer materials, nylon or other rigid plastics and can be reinforcedwith fiber to further control flexibility and feel.

Referring now to FIG. 10, an isometric view of a portion of theunderside of one piece platform 12 is shown in which one or more wedges82 are positioned within and between sidewalls 52 and 54 and transverserib 56. Wedges 82 may preferably be made of an elastomeric material andserve to reduce the twisting flexibility narrow section 22 of platform12 by, for example, resisting twisting motion of side walls 52 and 54.In a preferred embodiment, wedges 82 may be removably secured to thebottom side of one piece platform 12 by tightly fitting between thesidewalls or by use of screws or clips. The addition or removal ofwedges 82 changes the flexure characteristics of platform 12 andtherefore the feel or controllability of board 10. For example, wedges82 may be added for use by a beginning user and later removed forgreater control of board 10.

Referring now to FIG. 11, a partial view of self centering front section84, of one piece flexible board 10, in which caster wheel assembly 86 ismounted to hollow wedge 88 formed underneath front foot support 90 ofboard 10. Through bolt 92, only the head of which is visible in thisfigure, may be positioned through the inner race of wheel assemblysteering bearing 94, top or cap bearing 95 and the lower surface ofwedge 88 and captured with a nut, not visible here, accessible from thetop of platform 12 of board 10 in the hollow volume of wedge 88. Theouter race of bearing 94 is affixed to fork 96 of caster wheel assembly86, which is mounted by bearing 94 for rotation with respect to topbearing 95, so that wheel assembly 86 can swivel or turn about thecentral axis (shown as turning axis 34 in FIG. 2) of through bolt 92which serves as pivot axis 34 with respect to the fixed portions ofboard 10. Axle bolt 98 is mounted through trailing end 100 of fork 96 tosupport bearing and wheel assembly 102 for rotation of wheel 104.

In a preferred embodiment, a spring action device may be mounted betweencaster wheel assembly and some fixed portion of platform 12 (or of aportion of a caster assembly fixed thereto) to control the turning offork 96 and therefore caster wheel assembly 86 about turning axis 34 toadd resistance to pivoting or turning as a function of the angle of turnand/or preferably make caster wheel assembly self centering. The selfcentering aspects of caster wheel assembly 86 tends to align wheel 104with long axis 28 (visible in FIG. 1) when the weight is removed fromboard 10, for example, during a stunt such as a wheelie. Without theself-centering function of the spring action device, caster wheelassembly 86 may tend to spin about axis 34 through bolt 92 during awheelie so that caster wheel assembly may not be aligned with thedirection of travel of board 10 at the end of the wheelie when wheel 104makes contact with the ground. The self centering function of casterwheel assembly 86 improves the feel and handling of board 10, especiallyduring maneuvers and stunts, by tending to align wheel 104 with thedirection of travel when wheel 104 is not in contact with the ground.The spring action device may be configured to ad or not add appreciableresistance to maneuvers such as locomotion or turning when wheel 104 isin contact with the ground, depending on the desired relationshipbetween forces applied and the resultant twist of platform 12.

As shown in FIG. 11, caster wheel assembly 86 may be made self-centeringby adding coil spring 104 between fork 96 (or any other portion ofcaster wheel assembly 86 which rotates about the axis of bolt 92) andfront section 84 of platform 12 (or any other fixed portion of platform12).

Referring now to FIG. 12, a partial top view of caster wheel assembly 86is shown including bearing cap 95 (which is fixedly mounted by bolt 92to platform 12) and fork 96 (which mounted for rotation about axis 50through the center of bolt 92). In another preferred embodiment,self-centering of caster assembly 86 may be provided by a torsion springarrangement, such as helical torsion spring 106. A fixed end of helicaltorsion spring 106 may be fastened to a fixed part of board 10 such asbearing cap 95 or platform 12, while a movable end of helical torsionspring 106 may be mounted to a portion of caster wheel assembly 86mounted for rotation about axis 50 by for example fitting in a slot,such as notch 108 in fork 96.

Referring now to FIG. 13, a partial cross section view of the mountingfor rotation about axis 50 through caster bolt 92 of caster fork 96 isshown in which low friction bearing 110 is positioned between bearingcap 95 and the upper surface of fork 96. Low friction bearing 110 may bea solid, such as Teflon, or a liquid, such as a grease for bearing 94,or a combination of both. Further, low friction bearing 110 may merelybe an open space or cavity between bearing cap 95 and the top of fork 96which permits fork 96 to be supported solely by the outer race ofbearing 94 (visible in FIG. 11) without contact with bearing cap 95. Inany event, an open area such as cavity 112, surrounding bolt 92 andpositioned between the top of fork 96 and bearing cap 95, may beprovided in which torsion spring 114 may be mounted for causingself-steering of caster wheel assembly 86. In particular, torsion spring114 may include center section 116, such as a helical coil, a fixed end118 which may be fixed with regard to rotation about axis 50 by beingmounted through cavity 112 for penetration through bearing 110, ifpresent, into bearing cap 95, or into bolt 92. The other end 120 ofspring 114 is affixed to a portion of caster wheel assembly 86 whichrotates about axis 50 such as fork 96.

Referring now to FIGS. 14A-C, it is important to note that board 10 witha single piece twistable platform 12 and a self centering spring mayalso operate differently than board 10 without a self-centering spring.In particular, the self-centering spring may also provide a pivotalrotation dampening or limiting function which improves the feel of theride. FIGS. 14A and 14B are a pair of graphs illustrating board twistingangle as a function of the force applied by a user to twist platform 12.Horizontal axis 118, shown between FIGS. 14A and 14B, shows increasingforce which may be the force that can be applied by a user, in oppositedirections, to wider sections 18 and 20 to twist platform 12. Centerline120 of horizontal axis 118 represents zero force while the outer ends ofhorizontal axis 118 represent the maximum forces that a user would applyto wider sections 18 and 20 in opposite directions to twist platform 12.Each of the vertical axes 122 of the graphs represent the degrees oftwist of platform 12 at the ends of board 10.

Referring now to FIG. 14A, graph line 124 is used to represent the angleof twist of the ends of board 10 as a function of the force applied bythe user to a conventional, non-flexible single piece skateboard. Atzero point 126, there is no rotational twist even if there issubstantial differential force applied by the user's feet because in thecenter such differential force would be balanced and therefore therewould be not twist. With such conventional boards, the user may applysignificant differential pressure and there will be no, or very limited,end-to-end twist. The limited flexing of such conventional boards, ifany, is shown for example as an end-to-end twist on the order of perhapsabout 5° or less. The limited flexure or twisting available with suchconventional skateboards may be useful to absorb road bumps andvibrations in order to reduce stress and shock applied to the user'sfeet. This limited level of twist is not enough to provide substantiallocomotion or other advantages of a flexible one piece skateboard asdescribed herein. That is, even if the user were to complete severalcycles of applying differential force or pressure in a first sense (e.g.clockwise) and then in the opposite sense (e.g. counterclockwise), thelimited end-to-end twisting of the conventional board, if any, would notbe enough to rotate the direction casters (if used) about their pivotangles to provide any substantial tendency to locomotion of theskateboard.

Graph line 124 is shown for convenience as a straight line, and in someboards may represent a linear variation of end-to-end twist as afunction of differential force applied. However, in other boards, thefunction may not be linear and may for example better represented by acurve, such as a smooth curve.

Referring now to FIG. 14B, graph line 128 represents the angle of twistas a function of the differential pressure or force applied by the userto a flexible single piece board. Differential pressure or force may bethe force applied to twist platform 12, for example, by applying unequalforces on opposite sides of long or twisting axis 20. As noted above,the graph line may represent either a linear or non-linear function oftwist in response to differential applied force for one embodiment of asingle piece flexible board. Conventional operation zone 130 representsa portion of the graph line, centered around zero point 126, in whichdifferential pressure applied by the user will not produce sufficientend-to-end twist to cause any substantial tendency toward locomotion.The width of the conventional zone of operation zone represents themagnitude of the difference force or pressure which may be applied, forexample with one foot twisting the board in a clockwise direction whilethe other foot twists the board in a counterclockwise direction, thatcan be applied to board 10 without causing the board to operate as aflexible skateboard.

If this maximum differential or twisting force, that may be appliedwithout causing board 10 to operate as a flexible skateboard, to permitthe user to feel feedback or resistance from the board, the user canmore easily maintain a flat board, that is, to operate the board as aconventional board without causing board 10 to steer. Said another way,if the flexible board flexes easily about zero point 126 so that theuser can't easily distinguish by feel when the board is twistingsubstantially or not, the user may have to make continuous adjustmentsto the differential pressure applied to the board in order to have theboard run straight and true in a conventional manner. This range of lowlevels of differential pressure, if allowed to produce substantialend-to-end twist before the magnitude of the differential pressure iseasily noticed and/or controlled by the user, may be considered a “deadzone” and produce substantial user fatigue merely trying to keep theboard running straight. If however, as shown in graph line 128, therange of differential pressures (within which the end-to-end twist isnot enough to cause the skateboard to turn or otherwise operatenon-conventionally) is high enough so that the user can feel theresistance or feedback from the board, the board can easily be operatedto run straight without substantial user fatigue.

In other words, it may desirable for the board to provide sufficientresistance to initial twisting so that the user can feel the resistancewith his feet even when the differential pressure is low in order toreduce the fatigue and stress of operating a flexible board while goingstraight or steering only by tilted, as performed in a conventional,non-flexible or flat board manner. By applying more differential ortwisting forces, rolling energy can be applied to the wheels andlocomotion may still be accomplished by applying cycles of differentialpressures providing sufficient end-to-end twist beyond the conventionoperation zone 130 to cause locomotion and/or aid in steering the board.

Referring now to FIG. 14C, another important aspect of the twisting ofboard 10 may be that the amount of twisting of the material of board 10within each foot support area be minimized to reduce stress and fatiguefor the user. For example, if the twist within a foot support area ishigh enough, the twist may effect the vertical angle at which the user'sankle is supported. During twisting of the material of board 10, theheel and toe motion of user's feet causes twist. If the twist in eachfoot support area is high enough, the angle of support of the ankles tothe legs of the user be altered by the twist. For example, if it may beassumed for the purposes of discussion that all the twist in board 10 isperformed within narrow section 22, each foot support area may beconsidered to support the user's leg in a generally vertical plane eventhough, of course, the ankle may be rotated fore and aft and the knee isbent. If however, significant twisting also occurs within the footsupport area, for example if the user's leg is twisted further out ofthe vertical than would result if no twisting occurred within the footsupport area, operation of the board during twisting would likely causethe user greater stress and fatigue than would otherwise occur.

A small amount of twisting of within each foot support area may howeverbe acceptable. For convenience of illustration, user's shoe 19 is shownon foot position 18 of graph line 21 of board 10. The relative angle oftwist is shown along graph line 21 from central zero point 126. That is,board 10 is assumed to have a point within central section 22 whichhasn't rotated when the material of board 10 has been twisted to amaximum amount of twist, such as 50° of end-to-end-twist. The degrees ofrotation about twist axis 28 increase from zero point 126 to a maximumnumber of degrees, such as 22.5°, at the end of central section adjacentfoot support area 18. In order to reduce user's stress and fatigue, thechange from the vertical support (shown as dotted line 25), as a resultof twist of the material of platform 12 occurring within foot supportarea 18, of the user's leg above ankle 23, is limited to a small numberof degrees as illustrated by near vertical support line 27.

Referring again to FIG. 2, sidewall 62 may be used to reduce the fatigueor stress of the user resulting from a bending or bowing of surface 58of board 10. If the material of board 10 was too flexible, or notsufficiently support for example by sidewall 62 or the like to preventbowing, the user would experience stress on his ankles if his stood toofar outside of the area of support of wheel assemblies 24 and 26 becausethe outside of his feet would each tilt downward. Similarly, if the userstood too far inside of the support of wheel assemblies 24 and 26, hisankles would be stressed because the inside of his feet would tend totilt downward. The tilting of the user's feet from bowing of thematerial of board 10 can be said to occur generally in a plane acrossthe width of the user's body. A similarly stress may occur if too muchtwisting occurs within foot support areas 18 and 20. These stresseswould occur as a result of a shift in the support of the user's legs toofar from the vertical towards a direction part way between the planeacross the width of the user's body towards a plane through each of theuser's bent legs. The relative wider areas of foot support 18 and 20,compared to central section, may therefore also serve to reduce user'sfatigue or stress in a similar manner as the increased height ofsidewall 62 but as a result of preventing or reducing a different stressfactor. For purpose of explanation, the stress on the user's footresulting from excess twisting within a foot support area may be thoughtof as a twisting of the user's foot in which a forward part of theoutside or inside of the foot is twisted up or down more than a rearwardpart of that foot.

Referring now to FIG. 15 (as well as FIGS. 1, 2 and 11) top views offront and rear directional caster wheel assemblies 24 and 26 are shownin FIG. 15 aligned along twisting or long axis 28 of the top surface 12of board 10, shown in FIG. 1. In particular, in rear caster assembly 26,inner race 132 of bearing 94 is mounted to a fixed portion of theskateboard such as platform 12 while outer race 134 supports fork 96 inwhich rear wheel 36 is mounted for rotation about axle 40. The directionof rolling motion of caster 26 is perpendicular to axle 40 and isindicated as direction vector 140.

Bearing 94 is typically circular, but is shown in the figure in an ovalshape because this figure is a top view and outer race 134 is mountedfor pivoting rotation about axis 50 which is not orthogonal to topsurface 58 of platform 12 but rather at an acute trailing angle θ2 to itas shown for example in FIG. 2. The plane of bearing 94 is orthogonal toaxis 50 and therefore appears oval in this figure. Top points “T” andbottom points “B” of inner and outer races 132 and 134 are shown forease of discussion of the orientation of caster wheel assembly 26. Inparticular, wedge 48, which may be hollow, is mounted with its thickerportion forward so that top point T of inner race 132 is closer to topsurface 58 and bottom point B of inner race 132 is further away from topsurface 58 because of the acute trailing angle θ2 of axis 50.

The range of pivotal rotation of outer race 134 about axis 50 may belimited, for example, by self centering spring 106 (shown for example inFIG. 11) if present. Bearing 94, mounted in a plane at an angle to topsurface 58 as a result of wedge 48, tends to permit rotation so that toppoints T and bottom points B of the inner and outer races 132 arealigned.

In FIG. 15, the user is applying generally Ff 138 and Fr 136 (at frontand rear foot positions 14 and 16) generally along centerline or longaxis 28 as a result of which there is no differential force applied sothat there is no substantial end-to-end twist applied to top platform 12of board 10. In practice, if the level of resistance to twist ofplatform 12 is relatively low, e.g. so low that it is difficult for theuser to feel enough feedback from the resistance to twisting of platform12 to conveniently sense when no differential pressure is being applied,the user must work the board by applying varying amounts of differentialpressure in response to non-straight motions of the board. The constantworking of the board is undesirable because it causes fatigue andstress, so at least a minimum level of resistance to twisting may bedesirable in a single piece, flexible skateboard.

Referring now to FIG. 16, caster wheel assemblies 24 and 26 are showngenerally in the same way as shown in FIG. 15 except that front and rearfoot forces or pressures Ff 138 and Fr 136 are shown applied displacedin opposite directions from twisting axis 28. In one preferredembodiment, the resistance to twisting of platform 12 may besufficiently high that the user can easily apply at least somedifferential pressure to platform 12 without causing casters 24 and 26to turn from a straight forward alignment, that is, front and rearwheels 36 may generally maintain track with long axis 28 so that board10 operates as a conventional non-flexible board even though sufficientdifferential pressure may be applied by the user to get force feedbackfrom the board's resistance to twist. As shown by motion vector 140,which is aligned with long axis 28, board 10 may run straight, i.e.operate in a convention non-flexible board manner even with some applieddifferential foot forces as shown. This higher level of resistance totwisting may be desirable to reduce user fatigue and/or stress.

Referring now to FIG. 17, the user is applying substantialnon-differential pressure as indicated by Fr 136 and Ff 138 which causesplatform 12 to tilt. As a result, top point T and bottom point B of theinner races of bearings 94 of caster assemblies 26 and 24 are shifted bythe tilt in the opposite direction from the side of long axis 28 onwhich forces 136 and 138. In response, the applied forces cause thepivotable portions of the caster assemblies to pivot about their axes inorder for top points T and bottom points B of the outer races to becomealigned with the top points T and bottom points B of the inner races, asshown. Direction vectors 140, that is the paths that the wheels wouldtend to roll along, are no longer parallel with long axis 28 so thatboard 10 tends to change direction from the direction of axis 20 towardsthe direction of vectors 140. The actual turn resulting fromnon-differential forces 136 and 138 may depend on many factors,including the shape of wheels 36 as well as wobble and similar factors,but may be used at least in part for steering.

This above described operation of board 10 where steering of board 10results from a tilting of platform 12 may be considered to be within thezone of conventional operation of a non-flexible skateboard, that is,board 10 may feel to the user to be similar to the feel of aconventional board. It should be noted however, that, non-flexible,conventional skateboards using wedges and/or directional casters, maytypically be configured with the wedges facing in opposite directions sothat the rear wheel is forward of the rear wheel pivot point and thefront wheel is aft of the front wheel pivot point.

Referring now to FIG. 18, caster wheel displacement for such a design isshown for comparison. In such a configuration in which the pivot axes ofthe front wheels are not generally aligned with each other, e.g. thepivot axes are not both at a similar acute angle to top surface 12,non-differential foot pressure to the same side of long axis 28 maycause wheel 36 of front caster assembly 24 to rotate in a first sense(e.g. counterclockwise) as shown while causing wheel 124 of reardirectional caster assembly 144 to rotate in the opposite sense (e.g.clockwise) as shown. The resultant turn as shown would becounterclockwise, following the front wheel.

Referring now to FIG. 19, a flexible single board skateboard usingdirectional casters pivoted along generally aligned trailing axes may besteered by applying differential pressure, for example, forces Fr 136and Ff 138 to opposite sides of long axis 28 which causes thedirectional casters to rotate in opposite directions to steer and/orlocomote skateboard 10. It should be noted that in practice, board 10may well be steered using a combination of differential pressure ortwisting forces, as well as some level of tilt.

Referring now to FIGS. 14 through 19, in a preferred embodiment, theresistance to twisting of platform 12 may be sufficient to convenientlyoperate the skateboard in a straight line manner as shown in FIGS. 15and 16 with forces applied along long axis 28 or in a non-differentialmanner with roughly equal forces applied on opposite sides of long axis28. Similarly, board 10 may be steered by tilting platform 12 inresponse to applying forces from both feet to the same side of axis 28.These three operations may be considered as operations in conventionalzone 130 of FIG. 14, that is, operations which are the same or similarto operations of a non-flexible. The operation shown in FIG. 19 may beconsidered an operation outside conventional zone 130 in that twistingplatform 12 causes the wheel assembly to pivot in different directions.Platform 12 may also be tilted when twisted.

Single piece platform 12 may be configured from multiple pieces ofplastic material which are fastened together, for example by nuts andbolts, so that platform 12 twists as if it were molded from a singlepiece of plastic material.

Referring now to FIG. 20, flexible skateboard 146 may be configured witha single piece, molded wooden platform such as platform 148 with moldedin kick tail 150. Kick tail 150 is a portion of wooden platform 148extending well beyond rear wheel 152 so that a rider can apply pressurewith one foot to kick tail 150 to alter the performance of skateboard146 by for example kicking the tail of skateboard 146 down to contactthe ground to stop or alter the direction of travel. Wooden platform canconveniently be made by molding plywood by vacuum, steam or otherconventional processes. In addition to molding kick tail 150, it may beconvenient to mold in a symmetrical side to side shape as shown in FIG.21.

Referring now FIG. 21, a front view of a cross section of skateboard146, taken along line AA as shown in FIG. 20, illustrates one side toside shape which may be molded into wooden platform 148 of skateboard146 for example at kick tail 150 or along the length of platform 148.The illustrated cross sectional shape includes a center flat section 154

Referring now to FIG. 22, a top view of wooden platform 148 is shownillustrating the overall shape including the top view of kick tail 150.A preferred longitudinal grain direction for the wood or plywood fromwhich platform 148 is molded is illustrated by grain direction arrows158. A longitudinal grain direction will allow wooden platform 148 tobetter resist damage, for example by splintering, when twisted duringoperation of skateboard 146. The use of a longitudinal grain directionin the majority of the layers of a plywood board, for example the topand bottom layers of a 3 layer plywood board, used for making woodenplatform 148 may be particularly advantageous.

Referring now to FIG. 23, an isometric view of skateboard 146 includingkick tail 150 is provided for clarity.

Referring now to FIG. 24, a top view of an alternate embodiment is shownin which skateboard 160 may include a pair of center section inserts 162and 164 in a pair of through holes in platform 166 for controlling theflexure of platform 166. The inserts are shown in FIG. 24 positioned inthe pair of through holes which are positioned generally along theelongate axis of platform 166 and are shown bisected at the center ofskateboard 160. The pair of holes may be used, with or without inserts162 and 164, to alter the flexibility of skateboard 160 to twisting.Inserts 162 and 164 may be inserted in the holes to control theflexibility of platform 166. If the material from which the inserts aremade is more flexible than the material from which platform 166 is made,skateboard 160 would have more flexibility than if the inserts wereremoved, but less flexibility than if the holes were not present.

Similarly, if the material from which inserts 162 and 164 are made areless flexible than the material of platform 166, the presence of theinserts would tend to reduce the flexibility of skateboard 160 totwisting forces applied, for example, by a skateboard rider pumpingskateboard 160 to cause locomotion. The resilience of inserts 162 and164 may also be used to control or affect the operation of board 160.For example, if the inserts are made of a material which crushestemporarily when forces are applied, board 160 would flex differentlythan if the inserts were not present. In particular, board 160 wouldflex when twisting forces were applied more slowly than it would returnto its original shape when the twisting forces were removed because theoriginal twist would be resisted by the crushing of the foam, but thereturn would likely not be resisted by the foam because it would staycrushed at least for a short time.

Alternately, if inserts 162 and 164 were made of a springy rubber, thetwisting of board 160 would be affected by the response of the rubber,for example, springing back more quickly than if the inserts were notpresent. Further, under some circumstances it may be desirable to useonly one of the inserts. For example, if insert 162 were present withoutinsert 164, the flexibility of on end, such as the front, of skateboard160 can be controlled to be different than the flexibility of the rearof the board. That is, the flexibility of the board with respect totwisting forces applied by the leading foot of the skateboard ridercould be adjusted at least somewhat with respect to the flexibility ofthe board with respect to twisting applied by the other foot of therider. The wheels, not shown in the figure, under the front and rear ofplatform 166 allow forces applied to the front and rear sections of theboard to be at least to some degree somewhat isolated from each otherand thereby affected by the material of insert 162 and 164 if present.In a further embodiment, a different material may be used for inserts162 and 164 for more precise control of the relative flexibility of thefront and rear of the skateboard 160.

The rounded, somewhat dog-bone shape of the inserts and the holesthrough the platform in which they may be mounted reduces the likelihoodof stress fractures and weaknesses in platform 166 from flexure.

Referring now to FIG. 25, a single insert 168 may be positioned in asingle hole through the platform in lieu of the pair of inserts shown inFIG. 24 or the hole may be used without insert 168.

Referring now to FIGS. 26 through 29, a further embodiment is shown inwhich skateboard 170 includes platform 172 which may have a partialperipheral well along the outboard edges of the front and rear footpositions. A grip bar, such as rubber, may be positioned in theperipheral wells for better gripping by the rider's feet. The partialperipheral well may include an inner downward wall, a trough bottom, andan upward outer wall. The inner and outer peripheral well walls may beused to increase the resistance to flexing of the foot position portionsof platform 172. A pair of downward wall along the central section ofplatform 172 may be used to reducing the flexing of the central section.An insert may be positioned between the downward walls surrounding thecentral section of platform 172 to further control the flexing of thecentral section in response to twisting forces applied, for example, bythe rider.

Referring now more specifically to FIG. 26, platform 172 includes frontsection 174 and rear section 176 forming front and rear foot positions.A central area of the front and rear sections have a textured surface178 which may conveniently be formed in the material of platform 172when it is molded or otherwise formed. Platform 172 may preferably beformed of a molded plastic or wood, such as plywood, and therefore nothave as strong a gripping surface as may be desired at times for askateboard. Partial peripheral wells 180 and 182 may be formed along theouter edges along front section 174 while partial peripheral wells 184and 186 may be formed along the outer edges of rear section 176. Theperipheral wells may be filled with a material providing a good grippingsurface, such as rubber, for contact by the foot and/or heel of therider's feet. The material may be in the form of an insert which couldbe replaceable by the rider such as front and rear inserts 188, 190, 192and 194 respectively. The inserts may be made from rubber, plastic,metal alloys or similar materials.

In use, the shape and width of the rubber inserts may be configured sothat during normal riding, e.g. when skateboard 170 is being controlledin a straight and unbanked manner, or even while turning in a relativelygentle banked turn, the bulk of the user's weight may be applied tocentral areas 178 so that the user's feet may be quickly and easilymoved to change position of the rider's feet to change the forces beingapplied to the skateboard for control. In this way, the rider may alsoeasily change and adjust foot positions without a substantial grippingcontact with the rubber inserts.

During a maneuver, however, for example when the rider is applyingdownward pressure with the ball of one foot and the heel of the other,the additional pressure of the ball and heel applying the downwardpressure may preferably cause those portions of the rider's feet to makecontact with the rubber inserts, as well as the textured central areas,increasing the gripping force between the active portion of the foot andthe board. The contact, for example, between the ball of one of therider's feet with a gripping surface while that foot is applyingdownward pressure may provide useful additional control for the rider.In an optimal configuration, the rider may be able to control thegripping force by foot placement and pressure between the lower grippingforce when the rider's foot only contacts the textured surface of themolded platform and the greater gripping force when at least one portionof the rider's foot is also contacting the rubber insert.

Referring now also to FIG. 27 in greater detail, the upper surface ofrubber inserts 188, 190, 192 and 194 may be specifically textured, forexample, to increase the gripping force between the insert and therider's foot. Gripping projections 196 may be formed in the uppersurface of the rubber inserts to increase gripping forces. The materialfrom which the gripping projections, and/or the fill or insert material,may be selected to control the gripping force in light of the typical orexpected materials to be used on the soles of the rider's shoes.

Referring now also to FIG. 28 in greater detail, the underside ofplatform 172 is shown which may include ribbed central section 198,extending between troughs 200 of wells 180 and 182 of front section 174,for added strength. A similar configuration may be provided on theunderside of rear section 176 as shown. Ribbed section 198 is generallyunderneath central area 178 of front section 174 which may have surfacetexturing related to the ribbing and/or formed by the molding process.Wheel mounting structure 202 may be surrounded by and/or supported bythe ribbing in section 198.

The upward wall sections of well 180, for example, join together at walltransition point 204 and join a downward wall, such as sidewall or rib206 along the edge of skateboard central section 208. A pair of downwardwalls 206 form a portion of one or more chambers underneath skateboardcentral section 208 of platform 172 which may be filled by one or moreinserts, such as central insert 210. As discussed above in greaterdetail with respect to FIG. 10 and wedges 82, central insert 210 may beused to at least partially control the flexing of the skateboard and maybe inserted and/or removed by the rider based, for example, on therider's skill and/or difficulty of a particular maneuver.

Referring now in greater to FIG. 29, a cross section of front section174 is shown, taken along lines AA in FIG. 27. As shown the texturedcentral area 178 of front section 174 is generally flat but preferablyhas a slightly concave upwards shape for strength. Wheel mountingstructure 202 is positioned below central section 178 and may be atleast partially supported by ribs 198. Along the periphery of frontsection 174, partial peripheral well 180 is formed by inner downwardsidewall 212 along central section 178, trough bottom 214 and upwardouter sidewall 216. Rubber grip bar 188 may be positioned in well 180.The use of a pair of upward and downward sidewalls 212 and 216 mayprovide substantially greater strength, and/or resistance to twisting,for the front and rear sections of platform 172 than is easilyachievable using the same materials and a single sidewall as shown abovein the earlier figures. The use of the shape, material and fit of insertgrip bar 188 may also be used to control the resistance to twisting ofthe front and rear sections.

It should be noted that the use of upwardly open wells, such as partialperipheral well 180, joined at wall transition points, such as point204, to downwardly opening chambers such as central insert chamber 211,permits greater control of the resistance to twisting forces of thefront, central and rear sections 174, 208 and 176 respectively than theuse of a single wall as shown in earlier figures. In addition, therelative resistance to twisting between these sections of platform 172can also easily be controlled, so that the twisting may, for example, begenerally confined to the central sections and/or the front and/or rearsections of the skateboard. The use of inserts further enhances thecontrol of resistance to twisting forces of platform 172 and/or therelative resistance to twisting forces of the front, central and rearsections of platform 172 and provides the rider the ability to alter therelative and total resistance to twisting after purchase of skateboard170. Similarly, the transitions from a central downward facing sidewallto the pair of downward and upward facing sidewalls in which the outersidewalls transition directions, between upward and downward facing,twice on each side of skateboard 170, also greatly enhance the strengthand rigidity of the skateboard for a particularly size and material usedfor platform 174.

Referring now to FIGS. 30 and 31, an isometric view of one embodiment ofwheel assembly 86 is shown including centering spring assembly 222mounted within fork shell assembly 224. Wheel 226 is mounted to forkshell 224 for rotation about wheel rotation axis 228. Conventionalbearings and other hardware are not shown in this figure for clarity.Wheel assembly 218 may be bolted to skateboard 10, at an angled surfacesuch as wedge 32 to permit pivoting of wheel 226 about pivot axis 34 or50, as shown in FIG. 2, via internally threaded shaft 230. Fork shell224 may include bearing ring 232, the outer periphery of which may befastened fork shell 224 by for example spot welding.

Cartridge bearing assembly 234 may include an inner race mounted viacentering spring assembly 222 to prevent rotation against skateboard 10and an outer race mounted in a friction fit opening in bearing ring 232.As a result, fork shell 224 is mounted to the outer race of bearing 234for rotation about axis 34, 50 (which as described above are at an acuteangle to the plane of skateboard 10) while centering spring assemblymounted on the inner race of bearing 234 remains secured to—and does notrotate with respect to—skateboard 10.

Centering spring assembly 222 may include a threaded rod such as bolt236 which may be threaded into threaded shaft 230 through washer 238.Spacer 240 fits beneath washer 238 and around the shaft of bolt 236.Spring 242 has a preferably coiled central section which fits aroundspacer 240 coaxially with pivot axis 34 and within bottom cup 244. Whenbolt 236 is secured in threaded shaft 230, washer 238 may press againstthe top of spacer 240—and also against the partial outer rim of bottomcup 244—pushing bottom cup 244 against the inner race of cartridgebearing assembly 234 to maintain alignment and not rotate with respectto skateboard 10. Fork shell assembly 224 may rotate with the outer raceof cartridge bearing assembly 234 under the control of centering springassembly 222.

Referring now to FIG. 32, spring and bearing assembly 220 includescentering spring assembly 222 assembly and sealed type cartridge bearingassembly 234. Spring assembly 222 includes bolt 236, washer 238, spacer240, spring 242 having spring arms 246 and 248, as well as bottom cup244 having partial rim wall 250 with stops or edges 252 and 254. Edges252 and 254 may be on the order of 180° apart along partial rim wall 250and serve as stops 252, 254 for spring arms 246 and 248, respectively,when one of the spring arms attempts to move in the direction of theclosest stop. Further rotation of spring arms 246 and 248 is limited inthe other direction by fork assembly 224 and bearing ring 232 at stops272 and 276 as shown above in FIG. 30.

Cartridge bearing assembly 234 includes outer or bearing ring 232 whichmay be welded to fork shell assembly 224. Bearing outer race 256 may bepress fit in an opening in bearing ring 232 thereby supporting wheel 226in fork shell 224 for rotation about pivot axis 34, 50. Bearing innerrace 258 supports outer race 256, and therefore wheel assembly 86, forpivotal rotation. Bearing inner race 258 is compressed between washer238 and skateboard 10 by bolt 236 when assembled.

Referring now to FIG. 33, wheel assembly 218, supported by wheel bearingsupport 260 such as a ball bearing assembly, is mounted via wedge 32 toskateboard platform 12 by wheel mounting bolt assembly 262 for pivotalrotation of fork shell assembly 224 about pivot axis 34, 50. Shaft 230and inner race 258 of cartridge bearing assembly 232 are held rigidly toskateboard platform 12 and do not rotate while outer race 256, bearingring 232 and fork shell assembly 224 rotate about pivot axis 34, 50 whenforces are applied by actions of the rider which overcome the resistanceof centering spring assembly 222.

Referring now to FIG. 34, spring and bearing assembly 264 illustratesanother preferred embodiment of spring assembly 266 in which lowerspring arm 268 of coiled spring 270 extends generally at a right anglefrom spring assembly 266 to contact lower spring arm post 272 mounted onbearing ring 232. Bearing outer race 256 may be press fit in bearingring 232 which may support fork shell assembly 224—shown for example inFIGS. 30 and 31 above—for pivotal rotation about pivot axis 34, 50.Similarly, upper spring arm 274 of coiled spring 270 extends generallyat a right angle from centering spring assembly 266 to contact lowerspring arm post 276, which may also be mounted to bearing ring 256.

Coiled spring 270 is supported in centering spring assembly 266 aroundbolt 236 within bottom cup 244 which is pressed against bearing innerrace 256 (not visible under bottom cup 244 in this figure) by washer 238and spacer 240 (not visible behind spring 270) in this figure). Bolt 236is secured in threads not shown in threaded shaft 230 which may itselfbe secured to skateboard platform 12 as shown in FIG. 33. Wheel supportbearing 260 helps support bearing ring 232 for rotation about pivot axis34, 50.

Referring now to FIG. 35, an exploded view of spring and bearingassembly 264 mounted in bearing ring 232, bolt 236 is supported bywasher 232 which is supported by both space 240 and the partial rim ofcup 244. Spring 270 fits within cup 244 and includes a coil which fitsaround spacer 240. Cup 244 hand an opening formed by partial rim walledges 252 and 254. Lower spring arm 268 and upper spring arm 247 exitthe opening in cup 244 and in the travel straight ahead orientation orforward direction. Lower spring arm 268 contacts non-pivoting edge stop252 and pivoting post or stop 272 while upper spring arm 274 contactsnon-pivoting edge stop 254 and pivoting post or stop 276. Sealedcartridge bearing assembly 234 includes inner race bearing 258 inmounted for rotation within outer raced bearing 258. When assembled,bottom cup 244 is pressed against inner race bearing 258 which ispressed against skateboard 10 and/or wedge 32 and does not rotate withrespect to skateboard 10 while outer race bearing 256 may be press fitwithin and therefore mounted for rotation with bearing ring 232.

Referring now to FIG. 36, a top view of spring and bearing assembly 264is shown together with a portion of fork shell assembly 224 including adashed line portion of wheel 226 mounted for rotation about wheelrotation axis 228. Also shown in dashed lines is the upper portion ofpartial outer rim 278 of bottom cup 244 including rim wall edges ornon-pivoting stops 252 and 254. Inner bearing race 258 is not visible inthis figure beneath washer 238. Outer cartridge bearing race 256 isshown press fit within bearing rim 232 to which fork shell assembly 224may be affixed for pivotal rotation, by for example, spot welds 280.Upper and lower spring arm posts or stops 272 and 276 may also befastened by spot weld or other procedure to the top surface of bearingring 232 and/or fork shell assembly 224.

Spring 270, partially hidden in this figure under washer 238 but shownin more detail for example in FIG. 35, is captive within centeringspring assembly 266 around bolt 236 and/or spacer 240. Spring arms 268and 274 emerge from bottom cup 244 via the opening between rim walledges or stops 254 and 252, and are therefore visible in this figure.Spring and bearing assembly 264 is shown in the neutral or straightahead position in which the path of wheel 226 is along long or twistaxis 28 (shown for example in FIG. 1) of skateboard 10, that is,skateboard 10 is—or is oriented to—move in a straight line or forwarddirection.

In this position, upper and lower spring arms 274 and 268 may extend atabout right angles to pivot axis 34, 50— that is in an apparentlystraight line perpendicular to axis 34, 50—and are held from expandingto an angle greater than about 180° by rim wall edges 254 and 252respectively. During assembly of centering spring assembly 266, it maybe necessary to bring spring arms 268 and 274 together slightly to fitwithin the opening of bottom cup 244 between rim wall edges 252 and 254and then allow spring arms 268 and 274 to move apart again against rimwall edges 252 and 254 which operate as non-pivoting stops. As shownabove, bottom cup 244 is forced against inner bearing race 258 and doesnot rotate with respect to skateboard 10. Rim wall edges or stops 252and 254 therefore do not rotate with respect to skateboard 10.

Lower and upper spring arms 268 and 274, in the straight ahead positionshown in this figure, are also stopped up against lower and upper springarm posts or pivoting stops 272 and 276, respectively. Posts 272 and 276are secured to bearing ring 232 as shown or are in some other way causedto rotate with outer bearing race 256—and bearing ring 232 into whichthe periphery of outer bearing race 256 may be press fit—and fork shellassembly 224 which may be spot welded to bearing ring 232. In thestraight ahead position shown in this figure, lower spring arm 268 isstopped by both non-pivoting rim wall edge 254 and pivoting stop 272from expanding further away from upper spring arm 274 which is similarstopped by both non-pivoting both rim wall edge 254 and pivoting post orstop 276.

Referring now to FIG. 37, during operation of skateboard 10, for exampleduring steering toward the right (i.e. lower left edge of figure asshown), trailing caster wheel 226 will tend to pivot toward the left.Edges or stops 252 and 254 do not rotate with respect to skateboard 226,but posts or stops 272 and 276 are mounted for pivotal rotation withwheel 226 and will rotate for steering, for example in a counterclockwise fashion as shown in the view in the figure. Rim wall edge 254limits the rotation of upper spring arm 274, while stop 276 forces lowerspring arm 276 to rotate toward upper spring arm 274. As a result, thespring tension of spring 266 resists the pivot rotation of wheel 226about pivot axis 34, 50 so that when the forces causing caster wheel 226to pivot are removed, for example when skateboard 10 become airborneduring a maneuver after causing wheel 226 to pivot, the spring tensionof spring 266 presses upper spring 274 against rim wall edge or stop 254and rotates lower spring arm 268 against stop 276 until spring arm 268is stopped from further rotation by contact with rim wall edge 252 whenwheel 266 is again in the straight ahead or forward direction.

A similar resistance will be provided by spring 266 when forces areapplied causing wheel 226 to rotate about pivot axis in the other orclockwise direction so that whenever forces causing pivotal rotation ofeither front or rear caster wheels on skateboard 10 are removed, forexample when skateboard 10 becomes airborne, the caster wheels will bereturned to the straight ahead position as skateboard 10 returns to theground, greatly improving the rider's ability to make an acceptablelanding after an airborne maneuver.

Referring now again to the embodiment shown in FIGS. 30-33, as shown forexample in FIG. 30, spring arms 246 and 248 are pressed against theintersections of bearing ring 232 and fork shell assembly 224, acting asstops 272 and 276, and therefore operate in the same manner to resistpivoting of wheel 226 so that the wheel returns to the straight aheadriding direction aligned with long axis 28 before landing after anairborne maneuver. In fact, if either or both wheels become airborne,whether or not intentionally, they will return to the straight aheaddirection upon landing if they were pivoted about pivot axes 34 or 50before becoming airborne.

Referring now to FIG. 38, in operation, wheel mounting bolt assembly 262holds spring mounting cup 244 rigidly to skateboard 10 at a trailingacute angle along pivot axis 34, 50. Fork shell assembly 224 issupported for rotation about pivot axis 34, 50 by the outer race ofcartridge bearing 234 which supports fork 224 for rotation about theinner race of the cartridge bearing on which cup 244 is mounted and ballbearing 260 which supports fork 224 for rotation about the bottom ofskateboard 10 which is preferably the angled portion of wedge 32. Wheel226 is supported by fork 224 for rolling rotation about axis 228 andpivotal rotation about pivot axis 34,50.

When wheel 226 is oriented for straight ahead or forward movement ofskateboard 10, spring 266 maintains wheel 226 in this orientation bypressure of lower spring arm 268 against non-pivoting stop 252, whichmay be an edge of non rotating cup 244, and pivoting stop 272 whichrotates about pivot axis 34, 50 with fork 224. Spring 266 may preferablybe a multi-turn coiled torsion spring mounted in cup 244 coaxial withaxis 34, 50 including first spring arm 268, coil 282 and second springarm 274. Lower spring arm 268 may extend out from one end of coil 282through an opening in cup 244, at a right angle from axis 34, 50 tocontact stops 252 and 272 in the straight ahead position. Upper springarm 274 may extend out from another end of coil 282 through the openingin the side or rim wall of cup 244, for example at the end of coil 282through the opening in cup 244, for example at the end of spring coil282 away from skateboard 10, also at a right angle to axis 34, 50.

It should be noted that in this configuration spring arm 268 could beagainst non-pivoting stop 252 at a different position along axis 34, 50than arm 274 would be against non-pivoting stop 254. In a preferredembodiment, transition section 282 is used to position a terminal end ofarm 274 against pivoting stop 276 at generally the same position alongaxis 34, 50 at which arm 268 is against pivoting stop 272. As a result,the portion of arm 274 against pivoting stop 276 is in the same plane,transverse to pivot axis 34, 50, as the portion of arm 268 which isagainst pivoting stop 272.

When forces are applied to skateboard 10 to steer wheel 226 away fromthe straight ahead position as shown, for example to move the front ofwheel 226 toward the left of the drawing, spring 266 will resist pivotthis pivotal rotation because arm 268 is prevented from moving by stop252 and arm 274 resists movement of pivoting stop 276 mounted for motionwith fork 224 and wheel 226. When the forces applied to steer wheel 226to the left exceed the spring force applied by arm 274 against stop 276,fork 224 and wheel 226 may then rotate about axis 34, 50. In particular,when the forces applied by pivoting stop 276 exceed the spring forcesapplied by arm 274 and the right hand side of fork shell assembly 224,as shown in the figure, will move out of the plane of the figure towardthe viewer.

This rotation of fork 224 will cause arm 274 to move away from contactwith non-pivoting stop 254 which may be an edge of a rim wall of cup244. Similarly, this rotation of fork 224 will cause pivoting stop 272to move away from the viewer into the figure. Arm 268 will remainagainst non-pivoting stop 252 and will not move to follow pivoting stop272. As arm 274 is rotated about pivot axis 34, 50 in this manner, itwill rotate toward arm 268 in the same plane as arm 268. At apredetermined maximum angle of pivotal rotation, for example 180°, arm274 will contact arm 268 forcing it against non-pivoting stop 252.Further pivotal rotation of wheel 226 would be prevented. If the ends ofarms 268 and 274 are not in the same plane during pivotal rotation, theycould become tangled or otherwise not provide a clean maximum angle ofpivotal rotation and release from maximum pivotal rotation.

During operation when wheel 226 is caused to pivot about pivotal axis34, 50 by forces applied to or by skateboard 10, and wheel 226 becomesairborne, spring 266 and in particular coil 282, will cause wheel 226 toreturn to the straight ahead position. In the example described above,when wheel 226 becomes airborne or otherwise loses full or partialcontact with the ground, the forces applied to wheel 226 to pivot aboutaxis 34, 50 are reduced or removed. When the spring force applied by arm274 against pivoting stop 276 exceeds any remaining forces applied towheel 226 for pivotal rotation, spring 266 causes fork 224 to rotateback toward the plane of the paper until arm 274 contacts non-pivotingstop 254. Pivoting stop 272 would rotate out from behind the figuretoward the plane of the figure until pivoting stop 272 was again againstarm 268. In this orientation, with arm 268 again against both pivotingstop 272 and non pivoting stop 252, and arm 274 against both pivotingstop 276 and non-pivoting stop 254, fork 224 and wheel 226 would againbe oriented in the straight ahead position making contact between wheel226 and the ground much easier at the end of the maneuver.

One advantage of arms 274 and 268 being in the same plane occurs whenmaximum pivotal rotation occurs and skateboard 10 becomes airborne. Asmooth release of the maximum allowed pivoting rotation, e.g. arms 268and 274, not becoming entangled when released from contact with eachother, allows wheel 226 to more quickly and without hesitation return tothe straight ahead or neutral orientation when skateboard 10 becomesairborne.

Forces applied to steer or pivot wheel 226 in the opposite direction areopposed by spring forces applied by arm 268 to pivoting stop 274 andcause wheel 226 to return to the neutral position when the forces areremoved, for example when wheel 226 becomes airborne, or reduced belowthe spring forces, for example when at least some of the weight appliedby the rider to wheel 226 is shifted therefrom to the other wheel ofskateboard 10. This return spring assembly is preferably used with bothcaster wheels on skateboard 10 but may advantageously be used only withone such wheel under certain circumstances, for example, when the returnto neutral position action is better applied to only one wheel.

Referring now to FIGS. 39 and 40, additional views of spring and bearingassembly 264 with partially cutaway portion of fork 224 are shownincluding spring arm 274, stop 276, stop 254, bearing ring 232, outerrace 256, inner race 258, cup 244, washer 238, bolt 236, stop 252, stop272 and arm 268 are illustrated within a partially cutaway view of forkassembly 224 and wheel 226 to provide a perspective of the relativesizes, dimensions and relationship of the spring, bearing, fork andwheel components of one embodiment of the spring return caster describedherein.

Referring now to FIGS. 41 a-c, and also to the embodiments disclosed inFIGS. 31-40, operation of centering spring assembly 222 is illustratedwith skateboard 10 aligned in a forward direction in FIG. 41 a, withfork assembly 224 turned to an intermediate angle in thecounterclockwise direction in FIG. 41 b and to a predetermined maximumangle in the counterclockwise direction in FIG. 41 c.

As shown in FIG. 41 a, when skateboard platform 12 is moving in theforward direction, fork assembly 224 of wheel assembly 86 is orienteddirectly aft or behind the pivot axis—such as axis 34—by spring arms248, 246 which are against non-pivoting stops 252, 254 respectivelywhich are secured, for example to inner race 258 so the stops remainaligned with skateboard platform 12 and do not rotate during a steeringmaneuver. Direction tab 245, preferably on bottom cup 244, indicates theforward direction of skateboard 10 when caster wheel assembly 86 isproperly assembled and mounted on skateboard 10 and may be used in analignment fixture during assembly Maximum rotation of fork assembly 224on bearing ring 232 and outer race 256 is shown as angle 310 and maypreferably also be limited by contact between spring arms 248, 246 andpivoting stops 272, 276 as well as thrust cap fixed stops 300, 302 shownbelow in FIGS. 42 a-c.

As shown in FIG. 41 b, when for example skateboard 10 is being steeredby the user toward the user's right (shown as the left side of thefigure), fork assembly 224 may be caused to rotate counterclockwiseagainst the resisting force of spring arm 246 which is against rotatingor pivoting stop 272 which may conveniently be at one of theintersections between fork 224 and bearing ring 232. Spring arms 246,248 are preferably part of integral coiled spring 242 including springcoil 247. As fork assembly 224 is caused to rotate in a counterclockwisedirection, non-pivoting stop 254 prevents rotation of spring arm 248which allows outer race 256, bearing ring 232 and other pivotingportions of fork assembly 224 to rotate. That is, spring arm 246 resistscounterclockwise rotation of fork assembly 224 at intermediate angles byresisting counterclockwise rotation of stop 272, but spring arm 248 isagainst non-pivoting stop 254 allows stop 276 (at the intersection of aportion of fork shell 224 and bearing ring 232) to rotate away from arm248.

As shown in FIG. 41 c, counterclockwise steering rotation of forkassembly 224 may effectively be limited at a predetermined angle, suchas maximum steering angle 310 when pivoting stop 272 of fork assembly224, and spring arm 246, are rotated against spring arm 248 which isprevented from further rotation in the counterclockwise direction bynon-rotating stop 254.

Similarly, steering rotation in a clockwise direction is resisted byspring arm 248 and pivoting stop 276 via spring coil 247 andnon-pivoting stop 252 limiting clockwise steering rotation of spring arm246 until rotating stop 276 and spring arm 248 contact spring arm 246and/or non-pivoting stop 252.

If skateboard 10 becomes airborne during an intentional or unintentionalmaneuver while one or more fork assemblies 224 are pivoted in anydirection except the forward direction, each centering spring assembly222 causes each wheel 226, as shown for example in FIG. 30, to bealigned with long axis 28 to improve handling of skateboard 10 uponlanding.

Referring now also to FIGS. 42 a-c, a further set of positive stopsassociated with thrust bearing or bearing cap 95 at predeterminedmaximum steering rotation angles can be used together with and/or inlieu of the positive stop arrangement shown in FIGS. 41 a-c. As shownfor example in FIGS. 4, 11 and 13, top or thrust bearing 110 is formedbetween thrust bearing cap 95 and rotating top surface 70 of fork 42,96.

Referring now to FIG. 42 a, top bearing 110 is formed between topsurface 70 of fork 96 of fork assembly 224 and bearing cap 286. Theouter edge of a conventional thrust bearing cap has a series of flatedges, typically eight edges formed in an octagonal shape, so thatbearing cap 95 may easily be held or secured by a wrench, fixture orother tool for alignment. Hex head 288 of non-rotating threaded axle orshaft 290, shown below in greater detail in FIG. 43, secures fixed stopthrust bearing cap 286 against top surface 70 of fork assembly 224 tocapture a series of ball bearings—or other forms of bearingsurfaces—and/or a flexible seal not shown in this figure, to form top orthrust bearing 110.

Fixed stop bearing cap 286 has an outer edge with multiple surfaces fora tool, not shown, for use in orienting, securing and/or tighteningbearing cap 286 against top surface 70, with bearings 296 shown incutout opening 298 through bearing cap 286. Movable stops 300 and 302may be formed in a hexagonally shaped bearing cap 286 by removingmaterial along the periphery and/or originally stamping cap 286 in thisshape. Sufficient material of the periphery of cape 286 is missing orhas been removed so that rotating limit stop 304 may be positioned on anupper portion of fork assembly 224, such as top surface 70, withoutinterfering with steering rotation of fork assembly 224 until limit stop304 rotates into contact with fixed stop 300 or fixed stop 302. Limitstop 304 may conveniently be formed by punching out an “H” shapedopening 306 in top surface 70 and bending up rotating limit stop 304 asa tab.

As shown in FIG. 42 b, fork assembly 224 may be rotated in acounterclockwise direction by steering rotation about pivot axis 34until limit stop 304 attached thereto contacts fixed stop 302.

As shown in FIG. 42 c, fork assembly 224 may also be rotated in aclockwise direction by steering rotation about pivot axis 34 until limitstop 304 attached thereto contacts fixed stop 300. The total angular orsteering rotation of fork assembly 224 permitted by the interactionbetween limit stop 304 and fixed stops 300, 302 is angle 308. As show inFIGS. 41 a-c, the total angular steering rotation of fork assembly 224is angle 310 as a result of the interactions of spring arms 246 and 248with non-pivoting stop 252 or 254. In a preferred embodiment, steeringangle 310 will be at least a slightly larger angle than steering angle308 so that limit and fixed stops 304, 300 and 302 will provide apredetermined steering angle limit before contact between spring arms246 and 248 limits further steering rotation.

Referring now to FIG. 43, non-pivoting axle or shaft 290 mayconveniently be a partially threaded rod including external threadedsection 306 which may be secured to skateboard platform 12, for examplewithin hollow wedge 32 shown in FIG. 4. Fixed stop bearing cap 286 issecured to fork assembly 224 by hex 288 which may be integral on shaft290. As shown in FIGS. 42 a-c, dimples or welds on thrust bearing cap286 prevent cap 286 from rotating with respect to shaft 290 andtherefore with respect to skateboard platform 12. Shaft 290 maypreferably be coaxial with pivot axis 34 and include internally threadedsection 208. Fork assembly 224 and centering spring assembly 222 may bemounted for rotation to non-rotating shaft 290 by insertion ofinternally threaded section 308 tightly within a center aperture ininner race 258 of radial or cartridge bearing 234 secured by bolt 236,as shown for example in FIGS. 30 and 31.

Referring now to FIG. 44, a top view of dual wheel assembly 312 isillustrated that may be used in an alternate embodiment in replacementof one or both single wheel assemblies discussed above. Dual wheel forkassembly 314 is mounted for rotation about pivot axis 34 on shaft 290which may be fastened to an appropriate wedge—integral with, or mountedto—the skateboard to provide the desired acute angle of axis 34.

It may be advantageous to use the same mounting arrangements, as shownherein above or in variations thereof, so that one or two dual wheelassemblies may be interchanged with single wheel assemblies. The widerstance, or ground contact, of a dual wheel truck such as dual wheelassembly 312, makes the skateboard less lively and easier to control.This may be desirable in certain circumstances, such as during trainingon a skateboard or for particular stunts or procedures. Similarly, someusers may prefer to use a flexible skateboard with one or both wheelassemblies for other reasons, not requiring that the wheels beinterchangeable.

Wheels 316 and 318 are each affixed to wheel axle 320—mounted throughappropriate holes in fork arms 326 and 328 of fork assembly 314—by anysuitable retainer assembly, such as nut assembly 322. Wheels 316 and 318are separated by a fixed distance which, as shown in the figure indotted lines, may be approximately between 0 and 2 wheel widths as shownin the figure, depending on the degree of liveliness desired in theskateboard action. It may be convenient to include a suitable spacingcollar such as collar 324—which fits around wheel axis 320—between theopen ends of fork assembly 314.

A suitable bearing assembly, such as top bearing 110 or other bearingdescribed herein, may be used. It may be advantageous to use top bearing110 with the above described integral hard stops which also makes theskateboard easier to learn and handle as well as improve certainskateboard tricks.

Referring now to FIG. 45, an alternate embodiment of fork assembly 314is shown as fork assembly 315 in which fork arms 326 and 328, as well ascollar 324, may be replaced by forming one or more bends, such as bend336 in the sheet metal of fork assembly 315 as well as round retainingcollar 330 at one end of fork assembly 315 to mount axle 320 forrotation. One advantage of the use of bend 336 in fork assembly 315 isthat flexure about bend 336 may serve as a simple shock absorber makinglandings easier after a jump.

Referring now to FIG. 46, a side view of fork assembly 315 is shown inwhich one end of fork assembly 315 is mounted for rotation about pivotaxis 34 and secured against top bearing assembly 110 by nut 334 threadedon shaft 290. The other end of shaft 290 is held captive by nut 338,shown in dotted lines, inside wedge 32 integral with or fastened toskateboard platform 12. The other end of fork assembly 315 is formed inrolled retaining collar 330 shown in dashed lines behind wheel 318. Thenut normally threaded on axle 320 has been removed for clarity.

1. A skateboard, comprising: a skateboard platform of flexible material;a vertical support affixed to the platform to resist bowing from theweight of a rider; and a pair of wheels, each supporting one end of theplatform and mounted for rotation about a steering axis and about arotational axis; wherein twisting of the platform ends in oppositedirections by the rider propels the skateboard.
 2. The skateboard ofclaim 1 wherein the vertical support is a vertical wall extending belowthe platform.
 3. The skateboard of claim 2 wherein the vertical supportextends along a periphery of the platform.
 4. The skateboard of claim 3wherein the vertical support is a wall extending along the entireperiphery of the platform.
 5. The skateboard of claim 1, wherein thesteering axis of one wheel is at an acute angle to a surface of theplatform.
 6. The skateboard of claim 1, wherein the steering axis ofeach wheel is at an acute angle to a surface of the platform.
 7. Theskateboard of claim 1, wherein the steering axis of each wheel is at thesame acute angle to the surface of the platform.
 8. The skateboard ofclaim 1 wherein the rotational axis of one wheel is a first distancefrom the steering axis of that wheel.
 9. The skateboard of claim 1wherein the rotational axis of each wheel is at a distance from thesteering axis of said each wheel.
 10. The skateboard of claim 9, whereinthe rotational axis of each wheel is at the same distance from thesteering axis of said each wheel.
 11. The skateboard of claim 1 furthercomprises: a spring resisting steering of one of the wheels about thesteering axis thereof so that the one of the wheels can be centered bythe spring.
 12. The skateboard of claim 11 wherein the spring is mountedaround the steering axis.
 13. The skateboard of claim 12 furthercomprising: a pair of stops fixedly mounted to the platform; and atleast one limit stop mounted for steering rotation with the first orsecond wheel to prevent rotation of said wheel beyond a preset limit.14. The skateboard of claim 1 further comprising: additional verticalsupports below the platform.
 15. The skateboard of claim 1 wherein theflexible material is molded plastic.
 16. The skateboard of claim 1wherein the wall and platform are formed of the same material.
 17. Theskateboard of claim 1 wherein the flexible material is wood.
 18. Theskateboard of claim 17 wherein the wall and platform are formed of thesame material.
 19. A skateboard, comprising: a flexible, molded plasticskateboard; a vertical support molded to and extending below theplatform, the vertical support resisting bowing from the weight of arider and resisting twisting by the rider; and a pair of wheels, eachsupporting one end of the platform and mounted for steering rotationabout a steering axis at an acute axis to the platform and for rotationabout a rotational axis at a distance from the steering axis so thattwisting of the platform ends in opposite directions by the riderpropels the skateboard.
 20. The skateboard of claim 19 wherein thevertical support is a vertical wall extending below the platform along aperiphery thereof.
 21. The skateboard of claim 20 further comprises: aspring resisting steering rotation of one of the wheels to center thesteering rotation of the one of the wheels when not in contact with theground.
 22. The skateboard of claim 21 further comprising: a springresisting steering rotation of each of the wheels to center the steeringrotation of each of the wheels when not in contact with the ground. 23.The skateboard of claim 21 wherein the spring is mounted around thesteering axis.
 24. The skateboard of claim 23 further comprising: a pairof stops fixedly mounted to the platform; and at least one limit stopmounted for steering rotation with one of the wheels to prevent steeringrotation of said wheel beyond a preset limit.